OK so you are saying people use mineral oils because they are not as good, and the want the ring/piston to wear faster to speed up the running/bedding in process. Isnt that a risky option as you have no idea when to change, it could take 10 minutes or it could take 75 minutes. If it finishes in 10 minutes then the rest of the time is just wearing out a good motor.

How can a better oil damage an engine? Some mineral oils will damage the seals in an engine, as will some strange synthetics, but that will happen at any time you use the oil not just the first few minutes. The better lubrication qualities of synthetic oils will keep the motor cooler, and more importantly when the mixture is a bit too week, the oil is also reduced, synthetic oil will still keep working, as you dont nee anywhere near as much oil compared to Mineral oils.

Surly the best option with a new engine is to use the best posible oil, and use a higher ratio of oil to fuel rather than mess arround changing oils.

OK I can posibly go with that argument on an old motor where the cylinder has worn, or has been distorted due to overheating, and you want to fit a new ring/piston. But on a brand new motor, are you telling me the manufacturers do not make the cylinders round?

On plain bearing motors, like your average car engine, or the majority of Glow motors, I can take your point about the film strength as caster is just about the best oil for fourstroke motors. (not YS) All of the current petrol motors have roller bearing big and little ends, so there is no need to use mineral oils.

Changing oils can be quite risky as one or two synthetic oils do react with mineral oil and turn to glue. Unless you are sure the best thing on a new motor is to stay on the oil you plan to use.

Peter